The therapeutic use of pyrimidine nucleosides in the treatment of proliferative disorders has been well documented in the art. By way of example, commercially available antitumor agents of the pyrimidine series include 5-fluorouracil (Duschinsky, R., et al., J. Am. Chem. Soc., 79, 4559 (1957)), Tegafur (Hiller, S A., et al., Dokl. Akad. Nauk USSR, 176, 332 (1967)), UFT (Fujii, S., et al., Gann, 69, 763 (1978)), Carmofur (Hoshi, A., et al., Gann, 67, 725 (1976)), Doxyfluridine (Cook, A. F., et al., J. Med. Chem., 22, 1330 (1979)), Cytarabine (Evance, J. S., et al., Proc. Soc. Exp. Bio. Med., 106. 350 (1961)), Ancytabine (Hoshi, A., et al., Gann, 63, 353, (1972)) and Enocytabine (Aoshima, M., et al., Cancer Res., 36, 2726 (1976)).
Nucleoside analogues that show antimetabolic activity in cancer cells have been successfully used in the treatment of various human malignancies. Nucleosides such as 1-beta-D-arabinofuranosylcytosine (Ara-C), fludarabine and cladribine play an important role in the treatment of leukemias, while gemcitabine is extensively used in the treatment of many types of solid tumors. These compounds are metabolized in a similar manner to endogenous nucleosides and nucleotides. Active metabolites interfere with the de novo synthesis of nucleosides and nucleotides and/or inhibit DNA chain elongation after being incorporated into DNA strands, acting as chain terminators. Furthermore, nucleoside antimetabolites incorporated into DNA strands induce strand-breaks that may eventually result in induction of apoptosis.
Nucleoside antimetabolites target one or more specific enzyme(s) (Galmarini et al, Nucleoside analogues and nucleobases in cancer treatment. Lancet Oncol. 2002 July; 3(7):415-24; Review). The mode of inhibitory action on target enzymes may differ between nucleoside antimetabolites, which have the same nucleoside base, such as Ara-C and gemcitabine. Although both nucleosides are phosphorylated by deoxycytidine kinase and are also good substrates of cytidine deaminase, only gemcitabine shows antitumor activity against solid tumors. This suggests that there are differences in the pharmacological activity of these nucleoside antimetabolites, which may reflect different modes of action on target molecules.
It has been shown that dCK deficiency is associated with resistance to Ara-C in various cell and animal models (Galmarini et al, In vivo mechanisms of resistance to cytarabine in acute myeloid leukaemia, Br J Haematol. 2002 June; 117(4):860-8). Alterations in expression of the dCK gene or significant decrease in the activity of this enzyme in Ara-C-treated AML patients have also been correlated with clinical outcome. These data are consistent with the concept that intracellular phosphorylation of Ara-C by dCK is essential for cytotoxicity in cellular models and in patients. Deficiency of hENT1 in blast cell plasma membranes has also been suggested as a mechanism of cellular resistance to Ara-C. Other authors have suggested that mechanisms of drug resistance to Ara-C are associated with increased levels of Ara-C catabolic enzymes such as CDA.
EP 536936 (Sankyo Company Limited) discloses various 2′-cyano-2′-deoxy-derivatives of 1-β-D-arabinofuranosylcytosine which have been shown to exhibit valuable anti-tumour activity. One particular compound disclosed in EP 536936 is 2′-cyano-2′-deoxy-N4-palmitoyl-1-β-D-arabinofuranosylcytosine (referred to hereinafter as “sapacitabine”), this compound is currently under further investigation.
Sapacitabine, also known as CYC682 and 1-(2-C-cyano-2-dioxy-β-D-arabino-pentofuranosyl)-N4-palmitoyl cytosine (Hanaoka, K., et al, Int. J. Cancer, 1999:82:226-236; Donehower R, et al, Proc Am Soc Clin Oncol, 2000: abstract 764; Burch, P A, et al, Proc Am Soc Clin Oncol, 2001: abstract 364), is an orally administered novel 2′-deoxycytidine antimetabolite prodrug of the nucleoside CNDAC, 1-(2-C-cyano-2-deoxy-β-D-arabino-pentafuranosyl)-cytosine.

Sapacitabine has a unique mode of action over other nucleoside metabolites such as gemcitabine in that it has a spontaneous DNA strand breaking action, resulting in potent anti-tumour activity in a variety of cell lines, xenograft and metastatic cancer model (Hanaoka et al, 1999; Kaneko et al, 1997; Wu et al, 2003). Because of its unique mode of action, sapacitabine causes a block at the G2/M phase of the cell cycle rather than in S phase of the cell cycle, which is seen for gemcitabine and ara-C (Azuma et al 2001).
Sapacitabine has been the focus of a number of studies in view of its oral bioavailability and its improved activity over gemcitabine (the leading marketed nucleoside analogue) and 5-FU (a widely-used antimetabolite drug) based on preclinical data in solid tumours. Recently, investigators reported that sapacitabine exhibited strong anticancer activity in a model of colon cancer. In the same model, sapacitabine was found to be superior to either gemcitabine or 5-FU in terms of increasing survival and also preventing the spread of colon cancer metastases to the liver (Wu M, et al, Cancer Research, 2003:63:2477-2482). To date, phase I data from patients with a variety of cancers suggest that sapacitabine is well tolerated in humans, with myelosuppression as the dose limiting toxicity.
It well established in the art that active pharmaceutical agents can often be administered in combination in order to optimise the treatment regime. For example, combinations comprising a CDK inhibitor and 1-(2-C-cyano-2-dioxy-β-D-arabino-pentofuranosyl)-N4-palmitoyl cytosine, or a metabolite thereof, and their use in the treatment of proliferative disorders are disclosed in WO 2005/053699 (Cyclacel Limited).
The present invention seeks to provide new combinations of known pharmaceutical agents that are particularly suitable for the treatment of proliferative disorders, especially cancer. More specifically, the invention relates to combinations comprising 2′-cyano-2′-deoxy-N4-palmitoyl-1-β-D-arabinofuranosyl-cytosine, or a metabolite thereof, or a pharmaceutically acceptable salt thereof, with various cytotoxic drugs.
Although 2′-cyano-2′-deoxy-N4-palmitoyl-1-β-D-arabinofuranosyl-cytosine and these cytotoxic drugs are well established in the art as individual therapeutic agents, to date there has been no suggestion that the specific combinations claimed herein would be effective in the treatment of cancer.